1. Field of the Invention
The invention relates to an equalizer, and more particularly to an equalizer capable of providing tunable zero points.
2. Description of the Related Art
As signals propagate along a communication channel, such as a transmission cable, the input signals may be attenuated due to channel loss. The phenomenon especially occurs when long transmission cables are used, wherein the input signals may be seriously distorted and therefore cause intersymbol interference (ISI). In order to compensate for channel loss, an equalizer (or a zero forcing equalizer) may be adopted at the front end of a receiver to balance the channel loss. The equalizer is designed to invert the frequency response of the channel so as to remove the effect of the channel. The equalizer usually provides a zero (or called a zero point) at its frequency response to start boosting. FIG. 1 shows an exemplary frequency response of a communication channel. As shown, the frequency response of the channel begins to drop dramatically at point 101. Thus, a zero point may be designed corresponding to the frequency at point 101 so as to provide a starting position at which the gain of the frequency response of the equalizer starts to raise.
However, because different cable lengths and different cable materials cause different channel loss, an equalizer that is capable of providing a zero point with tunable zero values for dealing with different kinds of channel conditions is highly desired.